The goal of this project is to develop reliable indicators of normal syntactic develop for monolingual and bilingual children at ages before they begin to combine words in their own spontaneous utterances. Such measures would provide tests of normal language development in these populations so that infants at risk for disorders in syntactic development could be identified well before their own spoken utterances would show signs of specifically syntactic problems. Identifying children at risk for problems with developing syntax would allow for very early intervention for mental health problems that have been shown to accompany language disorders. Santelmann and Jusczyk (1998) used the Headturn Preference Procedure to demonstrate that 18-month old infants (but not 15-month-old infants) attend longer to natural sequences such as "Everybody is surely baking." I propose three series of experiments that extend S&J's work in ways necessary to document the normal morphosyntactic development of monolingual English-speaking homes and infants from bilingual Spanish/English-speaking homes. All of the experiments proposed that use Spanish stimuli test infants from bilingual Spanish/English homes. The first series of experiments investigates the nature and range of monolingual and bilingual infants' sensitivity to the morphosyntactic dependency between the verb "is" and predicates in English (i.e., V+ing, NP, PP, AP). The first study investigates whether the failure of 15-month old infants to differentiate natural and unnatural passages in S&J's original study is due to the low power in that study. The second study extends S&J's experiment to include other morphosyntactic dependencies into which "is" enters (i.e., PPs: Everyone is certainly in the room: NPs: "That man is surely a baker"; APs: "Everyone is very sad"). The third experiment examines the relative importance of closed class (e.g., "the") and open class (e.g., nouns" markers of syntactic elements that enter into a morphosyntactic dependency with "is" by testing whether children differentiate natural from unnatural passages with real nouns and nonsense determiners, and with nonsense nouns and real determiners. The fourth experiment tests whether infants are sensitive to the morphosyntactic relationship between "is" and "-ing" when such a dependency exists in an ungrammatical sentence (e.g., "Everyone is surely in the room-ing"). The second series of experiments investigates whether monolingual and bilingual infants are sensitive to two other types of morphosyntactic dependency in English: determiner-head noun number agreement within noun phrases (e.g., "The main saw a dog" vs "*The man saw a dogs"), and subject verb agreement infants raised in bilingual Spanish/English- speaking households are sensitive to this same range of morphosyntactic dependencies in Spanish, including agreement between "estar" (be) and "-ndo"(-ing), number and gender agreement between determiners and head nouns in noun phrases, and subject-verb agreement.